Surface Water Drainage Strategy

Earth Environmental & surface water drainage strategy
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What Type of Development Need a SuDS strategy?


  • Where the number of dwellings to be provided is 10 or more.
  • Where the development of dwellings is to be carried out on a site having an area of 0.5 hectares or more.
  • Where the provision of a building or buildings where the floor space to be created by the development is 1,000 square metres or more, or development carried out on a site having an area of 1 hectare or more.
  • Where there is a minor development of less than 10 dwellings located in areas at risk of flooding or in areas with critical drainage problems.
  • Where a number of small developments require SuDS reports even though they are not located in areas with flooding or drainage issues. This is often the case for small sites with an increase in impermeable areas.

SURFACE WATER DRAINAGE STRATEGY & SUDS

A surface water drainage strategy is a report detailing how surface water can affect a site and surrounding areas. It establishes how water can behave on a site, and estimates the surface runoff rate, viable flow pathways and likely sub-surface infiltration.

The surface water management strategy will also investigate what effect the development will have on these, and outlines measures the developer can take so that runoff rates meet the requirements for the site set by the National Planning Policy Framework (NPPF), the Environment Agency or by local planning policy.

In particular, the SuDS report will demonstrate that the development will conform to the guidance set out in NPPF where:

Paragraph 051 states, the drainage is to be designed to control surface water run off close to where it falls and mimic natural drainage as closely as possible, will provide opportunities to reduce the causes and impacts of flooding, and will remove pollutants from urban run-off at source;

As assessment will be carried out as stated in Paragraph 079 on whether a sustainable drainage system should be considered depending on the proposed development and its location;

And Paragraph 080 where the aim of the surface water management will be to discharge surface run off as high up the following hierarchy of drainage options as reasonably practicable: into the ground (infiltration); to a surface water body; to a surface water sewer, highway drain, or another drainage system; to a combined sewer.

The ‘Non-Statutory Technical Standards for Sustainable Drainage Systems – March 2015’ states that the post development surface water run-off rate should not exceed the pre-development greenfield rate, but where this is not reasonably practical the surface water run-off volume must be discharged at a rate that does not adversely affect flood risk.

What Do the Reports Detail?

  • Surface Water Run-off Calculations and reports. Assessment of Greenfield and Brownfield run-off rates and volumes pre and post development in accordance with best practice. Surface water run-off calculations are undertaken using the Institute of Hydrology (IH) 124 and Rational Methods.
  • Sustainable Drainage Systems (SuDS) Design. SuDS design in accordance with The SuDS Manual and BRE365.
  • Soakaway Design. Some small developments only require installation of soakways. Percolation test results subject to these being in accordance with BRE365 methodology.